Leecode 111.二叉树的最小深度

 /*
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int minDepth(TreeNode root) {
        //先判断是否为空
        if(root == null) {
            return 0;
        }
        int depth=0;
        Queue<TreeNode> que = new LinkedList<>();
        que.offer(root);
        while (!que.isEmpty()) {
            int len  = que.size();
            depth ++;
            for (int i = 0; i < len; i++) {
                TreeNode node = que.poll();
　　　　　　　//判断两个子节点都为空则为叶子节点
                if(node.right == null && node.left == null ){
                    return depth;
                }
                if(node.left != null) {que.offer(node.left);}
                if(node.right != null) {que.offer(node.right);}
            }
        }
        return depth;

    }
}